Plus

题号：NC237298
时间限制：C/C++/Rust/Pascal 1秒，其他语言2秒
空间限制：C/C++/Rust/Pascal 256 M，其他语言512 M
64bit IO Format: %lld

题目描述

Given $n$ , you need to find all pairs $(p,q)$ such that:

$1\leq p\leq q\leq n$ .
$p,q$ are all primes.
$p^q+q^p$ is a prime.

输入描述:

One line contains one integer . ()

输出描述:

In the first line, output the number of pairs $(p,q)$ you found.

Then each line contains two integers, indicating $p$ and $q$ .

If there are multiple pairs $(p,q)$ , you should output them in the increasing order. $(p_1,q_1)<(p_2,q_2)$ if and only if $p_1<p_2$ or ( $p_1=p_2$ and $q_1<q_2$ ).

示例1

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输出

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示例2

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